This application claims benefit of priority under 35 U.S.C. xc2xa7 119 to French Application Serial No. 97/16347, filed on Dec. 23, 1997 and claims priority under 35 U.S.C. xc2xa7 120 to Patent Cooperation Treaty Application Serial No. PCT/FR98/02853, filed on Dec. 23, 1998; the entire contents of which are incorporated by reference herein.
1. Field of the Invention
The present invention relates to a coil for planar transformer comprising at least one primary winding and at least one secondary winding, and more particularly such a coil of the type whose primary and secondary windings comprise turns made in the form of conductive tracks formed on the faces of a plane insulating support or of several stacked plane insulating supports connected together, as need be, by conductive holes passing through the plane insulating supports.
2. Discussion of the Background
In planar technology, a transformer winding, which is either primary or secondary, consists of at least two portions of conductive tracks made on different faces of one or several stacked plane insulating supports in such a way as to be able to exhibit connection terminals arranged on the periphery of the transformer, this being so as to ease electrical connecting of the transformer. The portions of conductive tracks of one and the same winding follow similarly directed spirals and are connected together electrically so as to ensure the continuity of the winding, by the inside ends of their spirals and, as need be, by certain of the outside ends of their spirals by means of conductive holes passing through the insulating support or supports.
According to current practice, the conductive tracks of the primary and secondary windings of a transformer are nested on the plane insulating supports so that there is an alternation of primary and secondary turns on any one of the plane insulating supports, on moving from the outside towards the centre of a transformer.
Although generally proving satisfactory, this solution has certain drawbacks.
Firstly, when one wishes to have different numbers of loops for the primary and for the secondary of a planar transformer, this being relatively frequent, it is necessary firstly to make, on one or several stacked plane insulating supports, primary and secondary windings with the same number of loops corresponding to the smallest of the numbers of loops required. Then to terminate the winding having the largest number of loops with complementary turns traced on one or several other plane insulating supports. This may lead to the use of a high number of stacked plane insulating supports whereas it is important to reduce the number of stacked plane insulating supports as far as possible for ease of construction.
Moreover, since the turns of the primary and secondary windings are alternated on the surface of the plane insulating supports, it is necessary to provide therebetween a spacing making it possible to ensure the desired electrical insulation between the primary and secondary of the transformer. Since the constraints of electrical insulation between primary and secondary of a transformer are often sizeable, this generally results in a non negligible spacing between each of the primary and secondary turns traced alternately on the surface of one and the same plane insulating support. This inter-turn spacing reduces the density of the turns, hence the number of turns which can be housed on a given surface of plane insulating support. Apart from the fact that it limits the possibilities for diminishing the bulkiness of the transformer, it reduces the magnetic coupling thereby causing an increase in the magnetic leakages. This results in a transformer which is less effective than one might hope for, especially as regards efficiency.
The present invention aims to alleviate these drawbacks.
To this end, the subject of the invention is a coil for planar transformer comprising at least one primary winding and at least one secondary winding with turns made in the form of conductive tracks formed on the faces of an insulating support and connected together by means of conductive holes drilled in the insulating support, characterized in that the portions of the primary and secondary windings carried by one and the same face of the insulating support are grouped together on a per-winding basis, according to two separate nested zones, of spiral shape, one of the zones grouping together, side by side, turns or portions of turns of the primary winding and the other zone grouping together, side by side, turns or portions of turns of the secondary winding.
Such a structure, although complex from the geometrical point of view, does not exhibit any more technological difficulties to be constructed than that of the prior art.
On the other hand, it makes it possible to construct on the two faces of one and the same plane insulating support, an entire coil, comprising primary and secondary windings having different numbers of loops. A transformer made according to the invention can therefore comprise fewer layers of supports, even if it generally has several of them, and consequently be less expensive and less voluminous.
It furthermore makes it possible to pack the turns closer together within one and the same zone on a plane insulating support face since they belong to one and the same primary or secondary winding for which the requirements of inter-turn insulation are always lesser than the requirements of insulation between primary and secondary windings. This makes it possible to improve the compactness of the transformer and hence to limit its magnetic losses.
In a particular embodiment of the invention, each winding portion forms a turn which extends over approximately 360xc2x0.
This layout has the advantage of being simple, since it leads easily to complete turns when two portions of winding are connected together electrically by a conductive hole joining the inside ends of their turns.
Also in a particular embodiment, one at least of the windings is formed on each face of the support of a plurality of winding portions joined successively from one face to the other of the support, in series by conductive holes.
It will be seen hereinbelow that this layout, which is also geometrically complex, makes it possible to arrange for numerous turns of the primary winding (respectively secondary winding) to be opposite the secondary winding (respectively primary winding).
Advantageously, the turns of each winding have shapes such that they create superposed indentations through which the conductive holes of the other winding pass.
Such an arrangement allows the best possible superposition of the primary and secondary windings, and it thus makes it possible to improve the magnetic performance of the transformer.
The subject of the present invention is also a multiple coil for planar transformer, comprising a plurality of coils as described hereinabove arranged one above another on a plurality of assembled supports, the primary and secondary windings respectively of the said coils being electrically linked to one another.
The said windings may then be linked either in series, or in parallel.
Provision may furthermore be made for several primaries and/or several secondaries.